When a hearing aid user experiences feedback, they’re experiencing the same phenomenon that occurs when a microphone is too close to a speaker. You may be familiar with the loud metallic sound it produces, and the wincing face of the speaker who experiences it.
When hearing aid microphones pick up amplified sound from the hearing aid unit and feed it back through the microphone, it can create a feedback loop that amplifies the audio signal until it becomes a high-pitched whine.
How Do Hearing Aids Handle Feedback?
Physical Design and Fit:
Correct fitting is critical. If you’ve ever used earbuds before and had to change the tips of your earbuds for a better fit, the principle is the same. Poorly fitting hearing aids, like earbuds, allow sound waves to enter the ear canal. This reduces the performance of the hearing aids and forces the brain to process additional background noise that isn’t present when a device is properly fit.
Hearing aid design matters. Well-designed hearing aids separate the microphone and the receiver. Vents allow some sound to escape. When vents are too large, they can leak audio from the receiver and create a feedback loop. Vents positioned and sized correctly can help your voice escape the ear canal while allowing natural sound to enter it.
Signal Processing:
Feedback cancellation cancels out sound. Sound waves can cancel one another through the process of destructive interference. When two sound waves of a similar frequency meet, but the peak of one sound wave meets the trough of the other, they can cancel each other out. This is called being ‘out-of-phase’. Hearing aids with cancellation features are equipped with technology similar to the ANC noise-cancellation found in headphones.
Adaptive feedback management monitors and adjusts sound. The onboard processors on hearing aids can provide real-time adaptive monitoring that adjusts amplification to filter out feedback. This can be especially helpful when sound sources are close to the ear, like during phone conversations.
Digital noise reduction is a similar technology that can identify and reduce background noise. This can help eliminate feedback while increasing the volume and clarity of speech.
The sensitivity of these systems can often be modified by an audiologist, who can help program your hearing aids for the environments you spend the most time in.
Is Feedback Technology Advancing?
Hearing aid manufacturers like Widex are constantly working to advance technology to enhance the clarity of sound. Their current models use a two-part feedback-cancelling system.
The Feedback Path Simulator
This continually monitors the part of the signal that is played back by the receiver. Continuous monitoring can remove portions of the signal that contribute to feedback before they get reamplified and cause a feedback loop.
The Dynamic Cancellation Optimizer
This analyzes the incoming signal. If the optimization system identifies audible feedback, the hearing aid will automatically reduce the gain of frequencies experiencing feedback.
These systems work together to provide a multi-tiered approach to feedback cancellation.
Would You Benefit from Better Feedback Cancellation?
If you have questions about your current hearing aid technology or whether an upgrade might add additional functionality, schedule with one of our specialists to learn more.